President Donald Trump called Elon Musk's plans to form a new political party "ridiculous," saying Musk could have fun with his new project but that the United States functions best under a two-party system.

"I am saddened to watch Elon Musk go completely "off the rails," essentially becoming a TRAIN WRECK over the past five weeks,' Trump wrote on social media.

Musk, who has been floating the idea of creating a third political party for weeks in the wake of his split with the president, reignited the push over the weekend after the passage of Trump's sweeping tax cut and spending bill -- which Musk railed against over its estimated impact adding trillions to the national debt.